The date of Earth’s first whiff of oxygen may have occurred 300 million to 400 million years earlier than scientists thought. According to an analysis of ancient sediment, hints of oxygen graced the Earth’s atmosphere around 3 billion years ago.

The new date places oxygen on the Earth more than 600 million years before the Great Oxidation Event, when levels of atmospheric oxygen rose dramatically. In the last six years, a handful of geologic studies have dated transient wisps of oxygen to 2.6 ...